Array substrate, method for fabricating and testing array substrate, and display device

ABSTRACT

The present invention provides an array substrate, which includes a plurality of pixel units, each pixel unit includes a thin film transistor, a pixel electrode, a common electrode and a passivation layer, the thin film transistor includes an active layer, a gate electrode, a source electrode and a drain electrode, the drain electrode and the pixel electrode are connected, the passivation layer is disposed on the active layer, the source electrode, the drain electrode and the pixel electrode, the common electrode is disposed above the pixel electrode with the passivation layer therebetween, a test electrode is disposed on the active layer and under the passivation layer, the test electrode is electrically insulated from the gate electrode, the source electrode and the drain electrode. Correspondingly, a method for fabricating and a method for testing the array substrate, and a display device including the array substrate are provided.

FIELD OF THE INVENTION

The present invention relates to the field of a display manufacturingtechnology, and particularly, to an array substrate, a display deviceincluding the array substrate, a method for fabricating the arraysubstrate and a method for testing the array substrate.

BACKGROUND OF THE INVENTION

With the development of a display manufacturing technology, a liquidcrystal display technology develops rapidly, it has replaced atraditional cathode-ray-tube display and become the mainstream of futureflat panel displays. In the field of the liquid crystal displaytechnology, Thin Film Transistor Liquid Crystal Displays (TFT-LCDs) arewidely used in televisions, computers, mobile phones and other areas dueto their advantages of large size, high integration, powerful functions,flexible manufacturing process and low cost. Wherein, a TFT-LCD of anAdvanced Super Dimension Switch (ADS, also referred to as ADSDS) modeforms a multiple dimension electric field by an electric field generatedby slit electrode edges in the same plane and an electrical fieldgenerated between slit electrode layer and plate electrode layer, inorder to enable the liquid crystal molecules with all orientationsbetween the slit electrodes in liquid crystal box and right above theelectrodes to rotate, and thus the operation efficiency of the liquidcrystal is improved and light transmission efficiency is increased,thereby increasing the picture quality of TFT-LCD products. Therefore,the TFT-LCD of an Advanced Super Dimension Switch mode is widely used inthe liquid crystal display area.

In a TFT-LCD, a display panel is the main component thereof, and isgenerally formed by aligning and assembling a manufactured arraysubstrate and a color filter substrate and then perfusing liquid crystalmolecules. In an ADS mode display panel, to detect whether the TFTchannel can be driven normally, a test on the TFT channelcharacteristics locating on the array substrate is required (generally,including tests on TFT switch current, threshold voltage and electronmobility. The specific test method is: connecting a probe of the testapparatus to a pixel electrode (the pixel electrode is located at theuppermost layer of the array substrate, and therefore the probe can bedirectly connected to the pixel electrode), as a drain electrode and thepixel electrode are connected, the probe of the test apparatus can beconnected to the drain electrode through the pixel electrode; theninputting corresponding signals into gate lines and data lines throughthe probe of the test apparatus, respectively; and determining whetherthe TFT channel can be normally driven according to the signal obtainedfrom the drain electrode by the test apparatus.

With the development of a TFT technology, a wide viewing angle panelcapable of being visible in the sunshine, i.e., High aperture ADS(H-ADS) mode display panel, comes forth in this area. In an arraysubstrate of an H-ADS mode display panel, as a pixel electrode islocated in the middle part of the array substrate (as shown in FIG. 1, apixel electrode 8 is located between a gate insulating layer 5 and apassivation layer 9), such that the probe of the test apparatus cannotbe connected to the pixel electrode or the drain electrode (the drainelectrode is also located in the middle part of the array substrate, asshown in FIG. 1, a drain electrode 7 b is located between an activelayer 6 and the passivation layer 9), and therefore, an existing testapparatus cannot be used to perform TFT channel characteristics test onthe H-ADS mode display panel.

SUMMARY OF THE INVENTION

In view of the above problems existing in the prior art, the technicalproblem to be solved by the present invention is to provide an arraysubstrate, a display device including the array substrate, a method forfabricating the array substrate and a method for testing the arraysubstrate, in which a TFT channel characteristics test can be performedusing an existing test apparatus.

The technical solutions used to solve the above technical problem are:

The array substrate includes a plurality of pixel units, each pixel unitincludes a thin film transistor, a pixel electrode, a common electrodeand a passivation layer, the thin film transistor includes an activelayer, a gate electrode, a source electrode and a drain electrode, thedrain electrode and the pixel electrode are connected, the passivationlayer covers the active layer, the source electrode, the drain electrodeand the pixel electrode, the common electrode is disposed above thepixel electrode with the passivation layer therebetween, a testelectrode is further disposed on the active layer and under thepassivation layer, the test electrode is electrically insulated from thegate electrode, the source electrode and the drain electrode.

Preferably, a via is provided at a position on the test electrode in thepassivation layer.

Preferably, the array substrate further includes a gate insulatinglayer; the gate insulating layer covers the gate electrode, and theactive layer is disposed on the gate insulating layer above the gateelectrode, and the source electrode and the drain electrode are disposedon the active layer, respectively.

Preferably, the array substrate further includes a gate insulatinglayer; the gate insulating layer covers the gate electrode, the sourceelectrode and the drain electrode are disposed on the gate insulatinglayer at two sides of the gate electrode, respectively, and the activelayer is disposed on the gate insulating layer above the gate electrodeand extends onto the source electrode and the drain electrode.

Preferably, the common electrode extends above the test electrode.

The present invention also provides a display device including theabove-described array substrate.

The present invention also provides a method for manufacturing the arraysubstrate, including steps:

1) forming a thin film transistor, a pixel electrode and a testelectrode on a substrate, the thin film transistor including an activelayer, a gate electrode, a source electrode and a drain electrode, thepixel electrode being connected to the drain electrode of the thin filmtransistor, the test electrode being formed on the active layer, and thetest electrode being electrically insulated from the gate electrode, thesource electrode and the drain electrode;

2) forming a passivation layer on the substrate subjected to step 1),the passivation layer covering the test electrode, the active layer, thesource electrode, the drain electrode and the pixel electrode;

3) forming a common electrode on the substrate subjected to step 2), thecommon electrode being disposed above the pixel electrode with thepassivation layer therebetween.

Preferably, the step 2) further includes a step of forming a via at aposition on the test electrode in the passivation layer.

Preferably, the step 1) further includes a step of forming a gateinsulating layer which includes forming the gate electrode on thesubstrate; forming the gate insulating layer on the gate electrode;forming the active layer on the gate insulating layer above the gateelectrode; forming the source electrode and the drain electrode on theactive layer, respectively.

Preferably, the step 1) further includes a step of forming a gateinsulating layer which includes forming the gate electrode on thesubstrate; forming the gate insulating layer on the gate electrode;forming the source electrode and the drain electrode on the gateinsulating layer at two sides of the gate electrode, respectively;forming the active layer on the gate insulting layer above the gateelectrode, and on the source electrode and the drain electrode.

Preferably, in the step 1), forming the test electrode, the sourceelectrode and the drain electrode in the same patterning process; thetest electrode is of the same material as the source electrode and thedrain electrode.

Preferably, the common electrode extends above the test electrode.

The present invention also provides a method for testing channelcharacteristics of the thin film transistor on the above-described arraysubstrate, and the method includes steps:

separating the common electrode on a pixel to be detected from thecommon electrode on the other pixels;

in the pixel to be detected, forming a via on the test electrode in thepassivation layer; and

electrically connecting the common electrode with the test electrodethrough an electrically conductive material layer in the via.

Preferably, the electrically conductive material layer is the commonelectrode which has covered the test electrode with the passivationlayer therebetween when manufacturing the array substrate.

Preferably, the via is formed on the test electrode in the passivationlayer by means of laser fusion, and the electrically conductive materiallayer is melted and flows into the via.

Preferably, the electrically conductive material layer is formed bydepositing electrically conductive material using a chemical vapordeposition (CVD) apparatus during testing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a structure of an array substrate inthe existing H-ADS mode display panel;

FIG. 2 is a flowchart of a method for fabricating the array substrate inembodiment 1 of the present invention;

FIG. 3 is a flowchart of a method for testing the array substrate inembodiment 1 of the present invention;

FIG. 4 (a) is a schematic diagram of the planar structure of the arraysubstrate according to embodiment 2 of the present invention, and FIG. 4(b) is a sectional view taken along a line A-A in FIG. 4 (a);

FIG. 5 is a flowchart of a method for fabricating the array substrate inembodiment 2 of the present invention;

FIG. 6 (a) is a schematic diagram of the planar structure of the arraysubstrate according to embodiment 3 of the present invention, and FIG. 6(b) is a sectional view taken along a line A-A in FIG. 6 (a);

FIG. 7 (a) is a schematic diagram of the planar structure of the arraysubstrate according to embodiment 4 of the present invention, and FIG. 7(b) is a sectional view taken along a line A-A in FIG. 7 (a); and

FIG. 8 is a schematic diagram of a structure of a thin film transistorin the array substrate according to embodiment 5 of the presentinvention.

In the figures: 1—substrate; 2—gate electrode; 3—gate line; 4—datalines; 5—gate insulating layer; 6—active layer; 7 a—source electrode; 7b—drain electrode; 8—pixel electrode; 9—passivation layer; 10—commonelectrode; 11—test electrode; 12—via.

DETAILED DESCRIPTION OF EMBODIMENTS

In order to enable persons skilled in the art to better understand thetechnical solutions of the present invention, the array substrate, thedisplay device including the array substrate, the method for fabricatingthe array substrate and the method for testing the array substrate willbe described in detail with reference to the accompanying drawings andspecific embodiments.

Embodiment 1:

This embodiment provides an array substrate, which includes multiplepixel units including thin film transistor (TFT), a test electrode, apixel electrode, a common electrode and a passivation layer; the thinfilm transistor includes an active layer, a gate electrode, a sourceelectrode and a drain electrode.

Wherein, the drain electrode is connected to the pixel electrode; thecommon electrode is disposed on the pixel electrode with the passivationlayer therebetween; the test electrode is disposed between the activelayer and the passivation layer, and the test electrode is electricallyinsulated from the gate electrode, the source electrode and the drainelectrode; the passivation layer covers the active layer, the testelectrode, the source electrode, the drain electrode and pixelelectrode.

This embodiment also provides a display device including theabove-described array substrate.

As shown in FIG. 2, this embodiment also provides a method forfabricating the above-described array substrate, including the followingsteps:

S100: preparing a substrate;

S101: forming a thin film transistor, a pixel electrode and a testelectrode on the substrate, the thin film transistor including an activelayer, a gate electrode, a source electrode and a drain electrode, thepixel electrode being connected to the drain electrode in the thin filmtransistor, the test electrode being formed on the active layer, and thetest electrode being electrically insulated from the gate electrode, thesource electrode and the drain electrode;

S102: forming a passivation layer on the substrate subjected to stepS101, and the passivation layer covering the test electrode, the activelayer, the source electrode, the drain electrode and the pixelelectrode;

S103: forming a common electrode on the substrate subjected to stepS102, the common electrode being disposed above the pixel electrode withthe passivation layer therebetween.

It should be noted that the method for fabricating the array substrateaccording to this embodiment does not limit the number of times ofpatterning process required to form the structures of respective layers.For example, the number of times of patterning process may be reduced byusing a half-tone mask plate or a gray tone mask plate, or the like.

As shown in FIG. 3, this embodiment also provides a test method fortesting the channel performance of the thin film transistor on theabove-described array substrate, including the following steps:

S201: separating the common electrode on a pixel to be detected from thecommon electrode on the other pixels. For example, the separation of thecommon electrodes may be achieved by using a laser cutting device.

S202: in the pixel to be detected, forming a via in the passivationlayer on the test electrode.

S203: electrically connecting the common electrode to the test electrodethrough an electrically conductive material layer in the via.

Preferably, the electrically conductive material layer is the commonelectrode which has already covered the test electrode with thepassivation layer therebetween during manufacturing.

Preferably, a via is formed on the test electrode in the passivationlayer by means of laser fusion, and the electrically conductive materiallayer is melted and flows into the via.

Preferably, the electrically conductive material layer is formed bydepositing electrically conductive material using a chemical vapordeposition (CVD) apparatus during testing.

That is, the way in which the common electrode and the test electrodeare electrically connected through the electrically conductive materiallayer has the following types:

The first way: when the common electrode is not disposed right above thetest electrode, and a via has already been formed in the passivationlayer on the test electrode, the common electrode can be electricallyconnected to the test electrode through the via by depositingelectrically conductive material.

The second way: when the common electrode covers the test electrode withthe passivation layer therebetween (i.e., the common electrode isdisposed right above the test electrode), a via is formed in thepassivation layer on the test electrode by means of laser fusion, andthe electrically conductive material layer is melted and flows into thevia such that the common electrode and the test electrode areelectrically connected through the via.

It can be seen that, the drain electrode and the active layer areelectrically connected (inherent characteristics of TFT), the activelayer and the test electrode are electrically connected, the testelectrode and the common electrode are electrically connected throughthe electrically conductive material, and therefore, the signal of thedrain electrode can be transmitted to the common electrode on the pixelto be detected, which has been separated from the common electrode onthe other pixels, of the array substrate surface. In practice, simplyconnect one probe of a test apparatus to the gate line (of course, thisprobe may also be connected to a circuit pin of the gate line drivingelement), connect one probe of the test apparatus to the data line (ofcourse, this probe may also be connected to a circuit pin of the dataline driving element), connect one probe of the test apparatus to thecommon electrode of the pixel to be detected, and input test signals tothe gate line and the data line respectively, and the channelperformance of the tested thin film transistor of the pixel to bedetected is thus obtained. As the size of TFT is relatively small, thesize of the drain electrode therein is smaller, but after the signal ofthe drain electrode is transmitted to the array substrate surfacethrough the common electrode on the pixel to be detected (which has beenseparated from the common electrode on the other pixels), on one hand,the probe of the test apparatus can directly collect the signal of thedrain electrode, and on the other hand, as relative to the size of TFT,the size of the common electrode on the pixel to be detected is muchlarger, the probe can easily be aligned, and therefore, the probe of thetest apparatus can collect the signal of the drain electrode moreeasily. It can be seen that it is possible to perform TFT channelcharacteristics test on the array substrate of this embodiment by onlyusing an existing test apparatus.

Embodiment 2:

As shown in FIGS. 4 (a) and 4 (b), this embodiment provides an arraysubstrate, including a substrate 1, a thin film transistor, a gate line3, a data line 4, a gate insulating layer 5, a pixel electrode 8, apassivation layer 9, a common electrode 10 and a test electrode 11. Thethin film transistor includes a gate electrode 2, an active layer 6, asource electrode 7 a and a drain electrode 7 b.

Wherein, the gate electrode 2 and the gate line 3 electrically connectedthereto are disposed on the substrate 1; the gate insulating layer 5covers the gate electrode 2 and extends onto the substrate 1; the activelayer (i.e., a semiconductor layer) 6 is disposed on the gate insulatinglayer 5 on the gate electrode 2; the source electrode 7 a, the drainelectrode 7 b and the test electrode 11 are disposed on the active layer6, respectively (that is, the source electrode 7 a, the drain electrode7 b and the test electrode 11 are electrically connected to the activelayer 6, respectively), a channel region (i.e., a TFT channel) is formedbetween the source electrode 7 a and the drain electrode 7 b, the testelectrode 11 may or may not be disposed at the channel region; the dataline 4 and the source electrode 7 a are electrically connected; thepixel electrode 8 is electrically connected to the drain electrode 7 band extends onto the gate insulating layer 5; the passivation layer 9covers the active layer 6, the test electrode 11, the source electrode 7a, the drain electrode 7 b and the pixel electrode 8, and extends on thegate insulating layer 5 such that the test electrode 11 is electricallyinsulated from the source electrode 7 a and the drain electrode 7 b, andthe gate electrode 2 is electrically insulated from the source electrode7 a, the drain electrode 7 b and the test electrode 11 through the gateinsulating layer 5; the common electrode 10 is disposed above the pixelelectrode 8 with the passivation layer 9 therebetween. In thisembodiment, the common electrode 10 is not disposed right above the testelectrode 11. Preferably, the distance between the test electrode 11 andthe source electrode 7 a equals to a half of the distance between thesource electrode 7 a and the drain electrode 7 b (i.e., TFT channelwidth).

This embodiment also provides a display device including theabove-described array substrate.

As shown in FIG. 5, this embodiment also provides a method forfabricating the above-described array substrate, including the followingsteps:

S300: preparing a substrate 1.

S301: forming a gate electrode 2 and a gate line 3 on the substrate 1.

Specifically, a gate metal thin film is formed on the substrate 1, thena layer of photoresist is coated thereon, and the photoresist is exposedusing a mask plate and is developed, etched and stripped to form thepatterns of the gate electrode 2 and the gate line 3.

The gate metal thin film can be formed using magnetron sputteringmethod, and its thickness range is 1000 Å˜7000 Å. The gate metal thinfilm can be made using a single-layer film of molybdenum, aluminum,aluminum-nickel alloy, molybdenum-tungsten alloy, chromium or copper, orusing a multiple-layer film formed by any combination of the abovemetals/alloys.

S302: sequentially forming a gate insulating layer 5 and an active layer6 on the substrate subjected to step S301, and disposing the activelayer 6 above the gate electrode 2 with the gate insulating layer 5therebetween.

Specifically, a gate insulating thin film and an amorphous silicon thinfilm are sequentially formed on the substrate subjected to step S301,then a layer of photoresist is coated thereon, and the photoresist isexposed using a mask plate and is developed, etched and stripped to formthe patterns of the gate insulating layer 5 and the active layer 6. Thegate insulating layer 5 functions as an etching blocking layer toprevent a damage to the pattern of the gate electrode 2 when forming thepattern of the active layer 6.

The gate insulating thin film and the amorphous silicon thin film can beformed using a chemical vapor deposition method. The thickness range ofthe gate insulating thin film is 1000 Å˜6000 Å, and the gate insulatingthin film can be made of silicon nitride, silicon oxide or siliconoxynitride. The thickness range of the amorphous silicon thin film is1000 Å˜6000 Å. Preferably, the amorphous silicon thin film is dry etchedto form the pattern of the active layer 6 (that is, forming a siliconisland).

S303: forming a source electrode 7 a, a drain electrode 7 b, a testelectrode 11 and data lines 4 on the substrate subjected to step S302,forming a channel region between the source electrode 7 a and the drainelectrode 7 b, and disposing the source electrode 7 a, the drainelectrode 7 b and the test electrode 11 on the active layer 6.

Specifically, a source-drain metal thin film is formed on the substratesubjected to step S302, then a layer of photoresist is coated thereon,and the photoresist is exposed using a mask plate and is developed,etched and stripped to form the patterns of the source electrode 7 a,the drain electrode 7 b, the test electrode 11 and the data lines 4, andthe source electrode 7 a and the drain electrode 7 b are formed on thetwo ends of the active layer respectively.

The source electrode 7 a, the drain electrode 7 b, the test electrode 11and the data lines 4 have the same slope angel after etching andthickness. The thickness range and the material of the source-drainmetal thin film are the same as those of the gate metal thin film.

S304: forming a pixel electrode 8 on the substrate subjected to stepS303, and electrically connecting the pixel electrode 8 to the drainelectrode 7 b.

Specifically, a pixel electrode thin film is formed on the substratesubjected to step S303, then a layer of photoresist is coated thereon,and the photoresist is exposed using a mask plate and is developed,etched and stripped to form the pattern of the pixel electrode 8.

The pixel electrode thin film can be formed using a chemical vapordeposition method, its thickness range is 100 Å˜1000 Å, and can be madeof Indium Tin Oxide (ITO) or Indium Zinc Oxide (IZO).

S305: forming a passivation layer 9 on the substrate subjected to stepS304, and making the passivation layer 9 cover the source electrode 7 a,the drain electrode 7 b, the test electrode 11 and the pixel electrode8.

Specifically, a passivation layer thin film is formed on the substratesubjected to step S304, then a layer of photoresist is coated thereon,and the photoresist is exposed using a mask plate and is developed,etched and stripped to form the pattern of the passivation layer 9.

The passivation layer thin film can be formed using a chemical vapordeposition method, its thickness range is 1000 Å˜6000 Å, and can be madeof silicon nitride or silicon dioxide.

S306: forming a common electrode 10 on the substrate subjected to stepS305, and disposing the common electrode 10 above the pixel electrode 8with the passivation layer 9 therebetween.

Specifically, a common electrode thin film is formed on the substratesubjected to step S305, then a layer of photoresist is coated thereon,and the photoresist is exposed using a mask plate and is developed,etched and stripped to form the pattern of the common electrode 10. Thethickness range and the material of the common electrode thin film arethe same as those of the pixel electrode thin film, respectively.

It can be seen that, compared to an existing manufacturing method, themethod for fabricating the array substrate of the present embodimentdoes not increase cost or the number of processes, and does not changethe materials of the multiple-layer structure of the array substrate.

The test method for testing the channel performance of the thin filmtransistor on the array substrate of this embodiment is the same as thatin Embodiment 1, and the way in which the common electrode and the testelectrode are electrically connected through the electrically conductivematerial layer may use the first way described in Embodiment 1, which isnot repeated here.

The other structures, methods and functions in this embodiment are thesame as those in Embodiment 1, and they are not repeated here.

Embodiment 3:

As shown in FIGS. 6 (a) and 6 (b), the difference between the arraysubstrate and the method for fabricating the array substrate of thisembodiment and those in Embodiment 2 is that: the common electrode 10extends above the test electrode 11, that is, the common electrode 10covers the test electrode 11 with the passivation layer 9 therebetween.

This embodiment also provides a display device including theabove-described array substrate.

The test method for testing the channel performance of the thin filmtransistor on the array substrate of this embodiment is the same as thatin Embodiment 1, and the way in which the common electrode and the testelectrode are electrically connected through the electrically conductivematerial layer may use the second way described in Embodiment 1, whichis not repeated here.

The other structures, methods and functions in this embodiment are thesame as those in Embodiment 2, and they are not repeated here.

Embodiment 4:

As shown in FIGS. 7( a) and 7 (b), the difference between the arraysubstrate and the method for fabricating the array substrate of thisembodiment and those in Embodiment 2 is that: the passivation layer 9has a via 12 disposed (formed) at the location on the test electrode 11.As the via has been formed in the passivation layer 9 in advance, thearray substrate with such structure will no longer need to form a viawhen the channel performance of the thin film transistor on the arraysubstrate with such structure is tested, which makes the test methodmore simple and easy.

This embodiment also provides a display device including theabove-described array substrate.

The test method for testing the channel performance of the thin filmtransistor on the array substrate of this embodiment is the same as thatin Embodiment 1, and the way in which the common electrode and the testelectrode are electrically connected through the electrically conductivematerial layer may use the first way described in Embodiment 1, which isnot repeated here.

The other structures, methods and functions in this embodiment are thesame as those in Embodiment 2, and they are not repeated here.

Embodiment 5:

As shown in FIG. 8, the difference between the array substrate of thisembodiment and that in each embodiment described above is that: thestructures of the thin film transistors are different.

Specifically, as shown in FIG. 8, the gate insulating layer 5 covers thegate electrode 2; the source electrode 7 a and the drain electrode 7 bare disposed on the gate insulating layer 5 on the two sides of the gateelectrode 2, respectively; the active layer 6 is disposed on the gateinsulating layer 5 which is on the gate electrode 2, and is disposed onthe source electrode 7 a and the drain electrode 7 b (that is, thesource electrode 7 a and the drain electrode 7 b are electricallyconnected to the active layer, respectively, and for facilitating theelectric connection between the pixel electrode 8 and the drainelectrode 7 b, the active layer 6 does not completely cover the drainelectrode 7 b).

The passivation layer 9 covers the active layer 6, and extends onto thesource electrode 7 a and the drain electrode 7 b which are notcompletely covered by the active layer 6, and onto the pixel electrode8; the common electrode 10 may or may not extend above the testelectrode 11.

Correspondingly, the differences between the method for fabricating thearray substrate of this embodiment and that in each embodiment describedabove are: forming the source electrode 7 a and the drain electrode 7 bon the gate insulating layer 5 on the two sides of the gate electrode 2,respectively; forming the active layer 6 on the gate insulating layer 5which is on the gate electrode 2, and on the source electrode 7 a andthe drain electrode 7 b.

The test method for testing the channel performance of the thin filmtransistor on the array substrate of this embodiment is the same as thatin Embodiment 1, and it is not repeated here.

It should be understood that, the above embodiments are exemplaryembodiments merely for illustrating the principles of the presentinvention, and the present invention is not limited thereto. Variousmodifications and improvements can be made by a person skilled in theart without departing from the spirit and substance of the presentinvention, and these modifications and improvements are also deemed asthe protection scope of the present invention.

The invention claimed is:
 1. An array substrate, including a pluralityof pixel units, each pixel unit including a thin film transistor, apixel electrode, a common electrode and a passivation layer, the thinfilm transistor including an active layer, a gate electrode, a sourceelectrode and a drain electrode, the drain electrode and the pixelelectrode being connected, the passivation layer covering the activelayer, the source electrode, the drain electrode and the pixelelectrode, the common electrode being disposed above the pixel electrodewith the passivation layer therebetween, wherein a test electrode isdisposed on the active layer and under the passivation layer andconfigured to test channel characteristics of the thin film transistor,and the test electrode is electrically insulated from the gateelectrode, the source electrode and the drain electrode.
 2. The arraysubstrate according to claim 1, wherein a via is provided at a positionon the test electrode in the passivation layer.
 3. The array substrateaccording to claim 1, wherein the array substrate further includes agate insulating layer; the gate insulating layer covers the gateelectrode, and the active layer is disposed on the gate insulating layerabove the gate electrode, and the source electrode and the drainelectrode are disposed on the active layer, respectively.
 4. The arraysubstrate according to claim 1, wherein the array substrate furtherincludes a gate insulating layer; the gate insulating layer covers thegate electrode, the source electrode and the drain electrode aredisposed on the gate insulating layer at two sides of the gateelectrode, respectively, and the active layer is disposed on the gateinsulating layer above the gate electrode and extends onto the sourceelectrode and the drain electrode.
 5. The array substrate according toclaim 1, wherein the common electrode extends above the test electrode.6. A method for testing channel characteristics of the thin filmtransistor on the array substrate according to claim 1, including steps:separating the common electrode on a pixel to be detected from thecommon electrode on the other pixels; in the pixel to be detected,forming a via on the test electrode in the passivation layer; andelectrically connecting the common electrode with the test electrodethrough an electrically conductive material layer in the via.
 7. Themethod according to claim 6, wherein the electrically conductivematerial layer is the common electrode which has covered the testelectrode with the passivation layer therebetween when fabricating thearray substrate.
 8. The method according to claim 7, wherein the via isformed on the test electrode in the passivation layer by means of laserfusion, and the electrically conductive material layer is melted andflows into the via.
 9. The method according to claim 6, wherein the viais formed on the test electrode in the passivation layer by means oflaser fusion, and the electrically conductive material layer is meltedand flows into the via.
 10. The method according to claim 6, wherein theelectrically conductive material layer is formed by depositingelectrically conductive material using a chemical vapor depositionapparatus during testing.
 11. A display device, including an arraysubstrate, the array substrate, including a plurality of pixel units,each pixel unit including a thin film transistor, a pixel electrode, acommon electrode and a passivation layer, the thin film transistorincluding an active layer, a gate electrode, a source electrode and adrain electrode, the drain electrode and the pixel electrode beingconnected, the passivation layer covering the active layer, the sourceelectrode, the drain electrode and the pixel electrode, the commonelectrode being disposed above the pixel electrode with the passivationlayer therebetween, wherein a test electrode is disposed on the activelayer and under the passivation layer and configured to test channelcharacteristics of the thin film transistor, and the test electrode iselectrically insulated from the gate electrode, the source electrode andthe drain electrode.